1. Field of the Invention
This Invention relates to a transparent heat-swellable material and to a fire-resistant glazing panel having multiple layers of glazing material with the said heat-swellable material bonded thereto.
2. Description of the Related Art
The general requirements for a fire-resistant panel are to provide an effective barrier against fumes and fumes and to provide thermal insulation. When all other parameters are constant, the extent of the fire resistance may depend on the type and size of glazing, the type of materials used in its construction and the manner in which it is held in a surrounding frame in an aperture. While glass is non-combustible it may itself soften or break under intense heat from a fire, or its frame may burn or distort, such that the barrier fails and direct fire propagation or escape of fumes can occur.
The use of a transparent heat-swellable material between layers of glazing material to improve the fire-resistant properties of glazing panels is well established to enhance the resistance of the panel both to heating in general and to exposure to fire in particular. The panel is formed as a laminate with a layer or layers of the transparent heat-swellable material each sandwiched between two transparent structural plies, usually thin glass sheets.
GB patent 1590837 teaches the use of an inturnescent material sandwiched between two structural plies in a laminated fire screening panel. It describes the use of hydrated metal salts as the inturnescent material especially hydrated alkali metal silicates such as hydrated sodium silicate. Later proposals have been concerned with modifying the silicate to improve its fire-resisting properties. For example WO94/04355 describes and claims a protective layer comprising a cured polysilicate prepared from an alkali metal silicate and a curing agent. EP-A-0705685 relates to a fire-resistant glazing panel comprising at least two glass sheets and an intermediate layer mainly composed of sodium water glass (sodium silicate) and water, together with hydrated potassium silicate and a small proportion of polyalcohols or sugars.
During the course of a fire, the silicate material slowly swells as the temperature increases, the water of hydration is driven off by the heat of the fire, and the material is converted to a foam which serves as a barrier to both radiated and conducted heat and may also preserve the ability to bond together structural sheets of the panel such as sheets of glass which may become shattered by the fire.
Panels are typically graded according to the length of time of heating under defined conditions until failure occurs in respect of such properties as insulation and integrity In the initial period of a fire, up to about 30 minutes, the panel should provide a high level of thermal insulation in order to facilitate the escape or if necessary the rescue of people in the affected area. This period is normally sufficient to permit the safe exit of everyone other than the fire-fighters who remain to control and extinguish the fire. The panel should also have sufficient integrity to provide a barrier to flame and fumes and a restraint to radiation of heat for at least the first 30 minutes and preferably for at least 60 minutes. With increasing emphasis on safety provisions in the home and at the workplace there is an increasing demand for panels to offer longer periods both of integrity, for example of 90 minutes or more, and of low radiation. Such longer periods are seen as important in seeking to provide sufficient time for fire-fighters to remain in a building and to control and extinguish the fire with minimum loss and damage to the affected property.
The fire-resistance of glazing panels is tested by mounting them in a wall of a furnace whose interior temperature is then increased according to a pre-determined schedule. Such a test is specified in International Standard ISO 834-1975 and is also described in International Standard ISO 9051-1990 which speaks specifically of the fire-resistance requirements for glazed assemblies, Similar European standards are proposed, including draft standard prEN1363 (document CEN/TC127 N 1095) and draft standard prEN1364 (document CEN/TC127 N 1085).
Draft standard prEN1363 includes a xe2x80x9cCotton wool padxe2x80x9d test and a xe2x80x9cGap gaugexe2x80x9d test. In the former a cotton wool pad in a frame is placed for a maximum of 30 seconds adjacent to an area of a test glazing specimen under examination for failure of integrity. The time and location at which any ignition of the pad occurs are recorded. In the latter a 6 mm gap gauge and a 25 mm gap gauge are in turn applied without undue force to determine (a) whether the 6 mm gauge can be passed through a gap in the specimen into the furnace and moved 150 mm along the gap and (b) whether the 25 mm gauge can be passed through a gap in the specimen into the furnace.
It is an objective of the present invention to provide a transparent heat-swellable material which offers for fire-resistant glazing panels a period of heat insulation and an extended period of fire-resistance, especially in terms of its xe2x80x9cintegrityxe2x80x9d, i.e. providing a barrier to flame and fumes, and of restrained radiation of heat. These features should moreover be provided without making the panel cumbersome and heavy.
According to this invention, there is provided a transparent heat-swellable material comprising hydrated alkali metal silicate and at least one additive selected from polyalcohols and mono- or polysaccharides, characterised in that the additive content is in the range 5 to 22% by weight, the water content is in the range 12 to 19.5% by weight, and the hydrated alkali metal silicate has a silicon oxide (SiO2):alkali metal oxide molar ratio greater than 3.3 to 1.
The invention further includes within its scope a sheet of transparent vitreous material carrying a layer of the above-defined heat-swellable material, and a fire-resistant panel comprising one or more layers of the said heat-swellable material and a corresponding two or more sheets of transparent vitreous material.
The term xe2x80x9cheat-swellablexe2x80x9d used herein refers to materials, otherwise known as inturnescent materials, with the properties, when exposed to a flame, of swelling and forming an insulating barrier to propagation of the flame.
The heat-swellable silicate materials of the invention offer considerable improvements in the thermal insulation, integrity (barrier to flame and fumes), and thermal radiation of glazing panels formed from them. The reasons for these improvements are not entirely clear but probably result from the combination of the claimed additive and an unusually low proportion of water. Another important factor appears to be that the silicates with a SiO2:alkali oxide molar ratio of greater than 3.3:1 expand less during standard fire tests than known materials obtained by drying alkaline silicate sols with a molar ratio of up to 3.3:1. The reduction in thermal radiation appears to result in part from the good integrity of the panel and the very low rates of flow of the foams arising from heat-swellable material according to the invention upon their exposure to fire.
The improvements are especially surprising in the case of soda-lime glass sheets which are commonly used in laminated glazing since the transformation temperature of the glass remains very largely below the temperatures reached during the fire tests; the transformation temperature of the foams in themselves is again largely less than that of the soda-lime glass.
The preferred alkali metal silicate is sodium silicate with a SiO2:Na2O molar ratio of about 4:1. A combination of this preferred silicate with a silicate having a lower SiO2:Na2O molar ratio, such as 3.3:1, also provides a panel with beneficial fire-resistant properties, provided that the total SiO2:Na2O molar ratio is greater than 3.3:1.
Preferred examples of the additive are glycerol ethylene glycol and saccharose. It is typically to be employed in an amount of 5 to 21% by weight of the transparent heat-swellable material. Glycerol is the most preferred additive. It is preferably employed in an amount of 10 to 16% by weight of the transparent heat-swellable material.
The water content of the said material should be in the range 12 to 19.5 %, typically 12 to 19 %, by weight. The preferred range is 15 to 19.5% by weight.
In one preferred embodiment the invention provides a transparent heat-swellable material comprising hydrated sodium silicate and glycerol, characterised in that the glycerol content is in the range 5 to 20% by weight, the water content is in the range 14 to 19% by weight, and the hydrated sodium silicate has a silicon oxide (SiO2):sodium oxide (Na2O) molar ratio greater than 3.3 to 1.
The panels according to the invention preferably include at least two layers of the said material and at least three layers of transparent vitreous material. A particularly preferred panel configuration comprises three layers of the said material and four layers of the transparent vitreous material.
As mentioned above, the transparent vitreous material is most typically soda-lime float glass and the present invention is primarily described with reference thereto. Other types of vitreous material for example borosilicate or aluminosilicate glass or of vitro-ceramic material, may however be employed for particular purposes, such as low expansion glass, extra-clear glass, hardened, armoured or coated glass. Usual plastics materials tend to be unsuitable for fire-resistant panels since they may ignite and may generate toxic fumes.
Panels according to the invention may be incorporated in double glazing and/or associated with polymer sheets or films. They may include a combination of thin and thick sheets of the transparent vitreous material. A thickness of less than 5 mm is preferred for each sheet of vitreous material in order to provide a panel which is thin, light and easy to install into a window or door frame.
The transparent heat-swellable material of the invention is preferably formed from a starting solution of hydrated alkali metal silicate and an additive. Care should be taken when preparing the starting solution to avoid agitation which would cause air or other gas to dissolve since these could reappear as microbubbles at a later stage. The solution is then partially dried to form a viscous material, known as a xe2x80x9csolid gelxe2x80x9d.
Thus the present invention further provides a method for the preparation of a transparent heat-swellable material from a starting solution of hydrated alkali metal silicate and at least one additive characterised in that the hydrated alkali metal silicate has a silicon oxide (SiO2):alkali metal oxide molar ratio of greater than 3.3 to 1, the additive is selected from polyalcohols and mono- or polysaccharides, and the solution is partially dried to form a solid gel having a content in the range 5 to 22% by weight, and a water content in the range 12 to 19.5% by weight.
In a preferred embodiment of the method of the present invention the starting solution is dried in such a way that the silicate product is in the form of grains. To form a glazing panel from this preferred granular form of the material, the grains are evenly distributed as a layer on a surface of a vitreous sheet. A second vitreous sheet is then placed on the grains, followed by further grain layers and sheets if required.
The maximum dimension of the grains is preferably in the range 10 to 700 xcexcm, most preferably in the range 150 to 500 xcexcm. These sizes facilitate formation of the grains into a compact layer with good optical and fire-resistance properties. Their beneficial effect on the behavior of the silicate layer during the course of a fire may possibly be the result of their achieving a fine and uniform foam structure when subjected to the intense heat of the fire.
Instead of converting the starting solution to granular form before application to the vitreous sheet, the solution can be applied directly to the sheet and then dried in situ thereon. The starring solution is highly viscous and its viscosity is increased by the drying, thereby assisting in keeping it in place.
The so-assembled panel is subjected to heat and pressure conditions to cause the silicate layer, whether formed from grains or directly from the solution, to bond to the respective adjacent surfaces of the vitreous sheets. The temperature for this stage is preferably at least 80xc2x0 C. and the applied internal pressure initially less than 30 kPa, as described in GB patent specification 2258422. In the case of a granular layer, the heat and pressure convert the grains into a continuous layer in which individual grains are not visible to the naked eye: the layer presents a uniform transparent appearance.
The heat and pressure also serve to degas the silicate product, thereby preventing the occurrence of visible gas micro-bubbles at or near the surface of the applied layer, which would otherwise adversely affect the optical properties of the layer and thus of the panel.
The panel is then subjected to further heating and pressure, typically in an autoclave, to complete the bonding.
To avoid bonding to the resulting silicate layer of any moulding plate used to compact the granular layer during assembly of a panel, the plate may be treated in an appropriate manner, for example with a silicone. In one convenient embodiment of the invention the moulding plate is constituted by, or faced with, a sheet which is to become incorporated into the panel and to which the silicate layer becomes bonded. The or each silicate layer may thus be sandwiched between two sheets of the panel which is simultaneously formed into a laminate by the heat and pressure treatment employed for the bonding. Indeed the whole panel may be assembled and formed into a laminate by that treatment.
The thickness of the or each layer of silicate material is preferably is in the range 0.1 to 5.0 mm. While layers as thin as 0.1 mm can give adequate short-term protection against fire, better protection is afforded by thicker layers. In general, increasing the thickness of such a layer beyond 5 mm does not give a commensurate increase in the degree of protection afforded and creates difficulties in achieving good optical properties.
In one embodiment of the invention the starting material includes an anti-ageing agent in an amount of up to 2% by weight. Preferably the anti-ageing agent is a quaternary ammonium compound, most preferably tetramethyl ammonium hydroxide (TMAH). The anti-ageing agent retards the ageing properties of the heat-swellable material which tend to occur as deterioration of the optical properties of the panel, for example a reduction in the transparency of the silicate.
The invention the offers fire-resistant panels having for example the following advantageous features in regard to the standards required of such panels:
a small (less than 20 mm) total panel thickness;
thermal insulation of greater than 30 minutes;
integrity (barrier to flames and fumes) of greater than 90 minutes; and a ratio of integrity to thermal insulation of more than 2;
thermal radiation of less than 10 kW/m2, or even of less than 6 kW/m2, after 90 minutes.
The combination of thermal insulation of greater than 30 minutes and thermal radiation of less than 10 kW/m2 after 90 minutes is a particularly advantageous feature of the invention.
The invention is further described in the following non-limiting examples.